Some chemical substances are known to show an effect of promoting the growth of a plant when applied to the plant. For example, aminolevulinic acid shows a growth promoting effect on a plant by application thereof.    (Nonpatent document 1) “Biosynthesis, biotechnological production and applications of 5-aminolevulinic acid” K. Sasaki et al., Applied Microbial Biotechnology 58: pp. 23-29    (Nonpatent document 2) The Pesticide Manual, Fifteenth Edition, British Crop Production Council (ISBN: 978-1-901396-18-8)